Hotend not heating up
July 19, 2021 01:27PM
So i have a pretty old printer (5years), i tried to run her after a long time .... i had replaced the extruder and then the hotend with a new one (E3d to MK8) while in the process i believe i shorted the 2 red wires coming out of the element at the hotend. After checking the V at D10 with a multimeter i got only 5v max, so i figured it must be the MOSFET, i replaced the MOSFET with the exact same one (IRF 3025) and am now getting 12V at D10, this is when the hotend is not commanded by marlin to heatup, after setting up a nozzel temp or preheating to PLA i still get 12V at D10 while it is commanded to heatup (also when idle) but the problem still there, the hotend doesnt heat up and ends up in THERMAL RUNAWAY (as expected), ALL other things work just perfect (including heating bed) ..... the thermistor is alright iv tested it with a heatgun

what i really don't understand is how come the hotend is not heating up when there is constant 12v ???

(my multimeter cannot measure Ohms precisely so i cannot check it for resistance and the max amp my multimeter can handle is 10a but ill still try to measure)

i dont think heater cartridge is at fault because it is brand new (never heated up) and iv checked the wires, they are covered properly at the element and dont seem to have any contact.


Any help is welcomed, regards 307
Re: Hotend not heating up
July 19, 2021 02:31PM
Ok so update : connected MOSFET D10+ with PS- (power supply ground) and got 12 v, the LED 3 or 4 is not lighting up as it is supposed to
connected MOSFET D8+ with PS- and got 12V
connected hotend with D8 and it heated up perfectly

So now i know the D10mosfet isnt working properly, but i doubt that it is a faulty mosfet as i just replaced it.... I think that the MOSFET isnt getting ON position.
Re: Hotend not heating up
July 19, 2021 02:51PM
Inspecting your solder connections, and the transistor insulating material if used is a good ideal!

Post a Picture of your mosfet show enough for us to inspect your replacement mosfet, maybe we can see something you have missed.

Edited 1 time(s). Last edit at 07/19/2021 03:02PM by Roberts_Clif.


Computer Programmer / Electronics Technician
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